The present invention relates to a power distribution control system in use for a vehicle (i.e. a 4 wheel-drive vehicle), which performs an appropriate control when a traction control unit; and a braking force control unit operate for controlling a vehicle motion behavior.
Recent vehicles are provided with a vehicle motion control unit, such as a traction control unit or a braking force control unit. The traction control unit secures improvements of acceleration, maneuvering stability and vehicle motion stability, when the vehicle starts to move by suppressing drive wheel spin. The braking force control unit appropriately controls a vehicle motion when the vehicle turns by applying a braking force to the wheel selected as intended.
Where the vehicle motion control unit is incorporated into the 4-wheel drive vehicle, the control by the vehicle motion control unit interferes with the control by a power distribution control system for the 4-wheel drive vehicle. Sometimes, this brings about an unfavorable situation for the vehicle. To cope with this, there is a proposal of a 4-wheel drive vehicle in which the 4-wheel drive is forcibly switched to a 2-wheel drive when the slip control is active (Refer to Japanese Patent Unexamined Publication No. Sho.61-37541).
However, when the 4-wheel drive is switched to the 2-wheel drive at the instant that the slip control becomes active, the running performance will remarkably be deteriorated. When the 4-wheel drive is switched to the 2-wheel drive, the vehicle characteristics abruptly change, and the driver may perceive a vastly uncomfortable drive feeling.
Accordingly, an object of the present invention is to provide a power distribution control system in use for a 4-wheel drive vehicle, in which even when a vehicle motion control unit operates and performs a vehicle motion control, an optimum power distribution control is continued without any excessive interference with the vehicle motion control, whereby an excellent drivability is secured without giving the driver any uncomfortable feeling.
The above object can be achieved by a power distribution control system for a vehicle(i.e. 4-wheel drive vehicle), according to a first aspect of the present invention, comprising a vehicle motion controller for controlling a motion of the vehicle, a power distribution controller and a clutch of a torque transmission capacity variable type operated by an operating torque set by the power distribution controller. The power distribution controller includes first torque setting means, second torque setting means and operating torque setting means. The first torque setting means computes a torque-response-torque that is based on an input torque received from a drive source and distributed to front and rear shafts. The second torque setting means computes a revolution-difference-response-torque based on a revolution-difference between a front shaft and a rear shaft. The operating torque setting means computes the operating torque using at least the torque-response-torque and the revolution-difference-response-torque. When the vehicle motion controller operates, the operating torque setting means computes the operating torque except the revolution-difference-response-torque.
The object of the invention may also be achieved by a power distribution control system for a vehicle (i.e. 4-wheel drive vehicle), according to a second aspect of the present invention, comprising a vehicle motion controller for controlling a motion of the vehicle and a clutch of a torque transmission capacity variable type operated by an operating torque set by the power distribution controller. The power distribution controller includes first torque setting means, second torque setting means, yaw-rate feedback torque setting means and operating torque setting means. The first torque setting means computes a torque-response-torque that is based on an input torque received from a drive source and distributed drive power to the front and rear shafts. The second torque setting means computes a revolution-difference-response-torque based on a revolution-difference between a front shaft and a rear shaft. The yaw-rate feedback torque setting means for computing a yaw rate feedback torque is based on a yawing state of the vehicle. The operating torque setting means computes the operating torque using at least the torque-response-torque, the revolution-difference-response-torque and the yaw rate feedback torque. When the vehicle motion control means operates, the operating torque setting means computes the operating torque except the revolution-difference-response-torque and the yaw rate feedback torque.
The object of the invention may also be achieved by a power distribution control system for a vehicle (i.e. 4-wheel drive vehicle), according to a third aspect of the present invention, whereby in the first or second aspect of the present invention, the vehicle motion controller controls a motion of the vehicle as intended by detecting a tendency of over steer of the vehicle and a tendency of understeer of the vehicle, and the operating torque setting means computes the operating torque; when the vehicle motion control means operates, in such a manner that correction quantities based on the oversteer and understeer tendency are added to the operating torque.
The object of the invention may also be achieved by a power distribution control system for a vehicle (i.e. 4-wheel drive vehicle), according to a fourth aspect of the present invention, whereby in the first or second aspect of the present invention, each of the correction quantities is selected depending on at least either of a vehicle speed and a road surface friction coefficient.
The object of the invention may also be achieved by a power distribution control system for a vehicle (i.e. 4-wheel drive vehicle), according to a fifth aspect of the present invention, whereby in the first or second aspect of the present invention, the operating torque setting means introduces a prescribed delay into a variation of the operating torque, when the operating torque is varied with the operation of the vehicle motion controller.
In the power distribution control system, according to the first aspect of the invention, the power distribution control means computes a torque-response-torque, which is based on an input torque received from a drive source for distributing the drive power to the front and rear wheels, by the first torque setting means. The power distribution control means computes a revolution-difference-response-torque based on a revolution-difference between the front shaft and the rear shaft by the second torque setting means. The power distribution control means computes operating torque using at least the torque-response-torque and the revolution-difference-response-torque by the differential torque setting means. Then a torque transmission capacity variable type clutch means is operated by the operating torque, so as to distribute drive power to the front and rear wheels. When the vehicle motion control means operates for controlling a vehicle motion as intended, the operating torque setting means of the power distribution control means computes the operating torque, except the revolution-difference-response-torque. The computed operating torque controls the torque transmission capacity variable clutch means. Accordingly, even when the vehicle motion control unit operates and performs a vehicle motion control, an optimum power distribution control is continued without any excessive interference with the vehicle motion control, whereby an excellent drivability is secured without giving the drive any uncomfortable feeling.
In the power distribution control system, according to the second aspect of the present invention, the power distribution control means computes a torque-response-torque, which is based on an input torque received from a drive source for distributing the drive power to the front and rear wheels by the first torque setting means. The power distribution control means computes a revolution-difference-response-torque based on a revolution-difference between the front shaft and the rear shaft by the second torque setting means. The power distribution control means computes a yaw rate feedback torque based on a yawing state of the vehicle by the yaw-rate feedback torque setting means. The power distribution control means computes a operating torque using at least the torque-response-torque by the operating torque setting means. Then, the torque transmission capacity variable clutch means is operated by the operating torque, to distribute drive power to the front and rear wheels. When the vehicle motion control means operates for controlling a vehicle motion as intended, the operating torque setting means of the power distribution control means computes the operating torque, except the revolution-difference-response-torque and the yaw rate feedback torque. The computed operating torque controls the torque transmission capacity variable type clutch means. Accordingly, even when the vehicle motion control unit operates and performs a vehicle motion control, an optimum power distribution control is continued without any excessive interference with the vehicle motion control, whereby an excellent drivability is secured without giving the drive any uncomfortable feeling.
In the power distribution control system, according to the third aspect of the present invention, when the vehicle motion control means controls a motion of the vehicle as intended by detecting a tendency of oversteer of the vehicle and a tendency of understeer of the vehicle, and the operating torque setting means computes the operating torque in such a manner that correction quantities based on the oversteer or understeer tendency are added to the operating torque when the vehicle motion control means operates. The vehicle motion control means also prevents the oversteer or the understeer tendency.
In the power distribution control system, according to the fourth aspect of the present invention, each correction quantity is selected depending on at least either a vehicle speed or a road surface friction coefficient. According to this correction quantity, the control precision is higher.
In the above power distribution control systems, according to the fifth aspect of the present invention, the operating torque setting means introduces a delay into a variation of the operating torque, when the operating torque is varied by the operation of the vehicle motion control means. A variation of the operating torque with the operation of the vehicle motion control means is made as gentle as possible, so that a variation of the vehicle characteristics caused by the variation of the power distribution to the front and rear wheels is made gentle.
The preferred embodiments of the present invention will be described with reference to accompanying drawings. FIGS. 1 to 4 are diagrams showing the preferred embodiments of the present invention. FIG. 1 is a block diagram showing an arrangement of an overall power distribution control system of a vehicle. FIG. 2 is a functional block diagram showing a front/rear drive force distribution control system. FIG. 3 graphically represents a variation of transfer clutch torque when a traction control operates. FIG. 4 is a flow chart of a front/rear drive force distribution control.